Perfluorelastomers have long been used in a variety of applications that require excellent resistance to high temperatures and chemical attack. A particularly outstanding class of fluoropolymers that has been used in elastomeric applications is that prepared from tetrafluoroethylene (TFE) and perfluoro (alkylvinylether) such as perfluoro (methylvinylether) (PMVE). To permit the crosslinking in these polymers that is essential to good elastomeric properties, a small percentage of termonomer is incorporated. A wide variety of such crosslinking sites has been used in the past, including those described in Brizzolara et al., U.S. Pat. No. 3,682,872.
One particularly desireable terpolymer is that prepared from TFE, PMVE and a nitrile cure site monomer, such as perfluoro (8-cyano-5-methyl-3,6-dioxa1-octene), or 8CNVE. This fluoropolymer has been cured in the past by organometallic compounds such as tetraphenyltin, which results in trimerization of the cyano function of the 8CNVE to triazine crosslinks. However, the high viscosity of the resulting compound and the slow rate of cure make the processing of this crosslinked material difficult. In addition, because the triazine crosslinks are prone to nucleophilic attack, they have inadequate resistance to aliphatic amines and water at elevated temperatures, particularly above 150.degree. C. Further improvement in these properties in the cured perfluoroelastomer has therefore been desired, along with improved processability. It would be also desirable to eliminate the need for the toxic organometallic compounds often used in the curing operation.
Accordingly, continuing effort has been directed to the development of curing systems which result in improved physical properties in the cured elastomer and which permit curing at the least stringent conditions.